The invention relates generally to radio frequency identification (RFID) tags. In particular, RFID tags able to respond to select first frequencies by reflection at select second frequencies.
Radio-Frequency IDentification (RFID) technology receives growing attention worldwide in a broad range of applications. RFID becomes one of the key elements to interface objects in the physical world. Many conventional RFID tags are passive and static. The communications between tags and readers are accomplished by electromagnetic waves of radio frequency. The reader's antenna sends the electromagnetic signal to the tag. The tag's antenna receives the signal and reflects the modified electromagnetic wave back to the reader. Then the reader receiver picks up the tag's radio waves and interprets the information as meaningful data. Static RFID is vulnerable, being susceptible to be detected, and the information being transmitted cannot be altered.
For some applications, a desirable capability enables the RFID code of the target can be changed dynamically. This type of RFID can avoid detection by an adversary to thereby enhance the capability of identifying friend and foe (IFF). Dynamic RFID tags use microchips to store data that are retransmitted when interrogated. Often the RFID tag is powered by the radio frequency (RF) signal received, but sometimes they are powered by batteries or other means. The information of the identification (ID) is coded in the modulation provided by the microchip. Each modulated signal corresponds to a unique identification that can be changed dynamically in response to different interrogators, for example.